This invention relates to a seawall system for controlling shoreline erosion and preventing damage to construction properties during coastal storms. More particularly, the invention is directed to an adaptable high energy return seawall system having a hydraulically dynamic design which effectively dissipates wave energy under severe storm conditions by causing the kinetic energy within waves to work against itself.
The tremendous power and energy of the sea is quite evident by the extent of destruction caused during coastal storms. When a high energy wave strikes an immovable object such as a vertical concrete structure or bulkhead, the generally clockwise motion of the wave causes most of its energy to go downwardly, producing a scouring action at the base of the structure or bulkhead. This scouring action is the main cause of erosion and results in the massive removal of gravel, sand and other sedimentary materials at the base, causing an overhang to develop which undermines the very foundation on which these structures are built. Any remaining energy from the same high intensity wave is absorbed by direct impact upon the structure or bulkhead itself and repeated wave action of this type causes the structure to weaken and oftentimes to crack under the compounded wave pressure. The intensity of coastal storms is directly related to shoreline erosion and as erosion accelerates, entire beaches and shoreline disappear, buildings and other constructions are washed away to sea, and displaced sand and gravel are carried away by undertows to form undesirable sandbars in channels and shipping lanes.
Various devices and techniques have been proposed in the prior art for protecting shorelines from erosion. One such device is disclosed in U.S. Pat. No. 1,811,055, issued May 23, 1930 to Forbes. This patent describes a seawall comprising a concrete superstructure of the "step and roll way type" and a foundation including a bulkhead and interlocking buttresses of sheet metal piling driven to a depth to prevent undermining by the scouring action of waves and currents. However, the patented device is difficult to construct and maintain, and is simply too expensive to be of any practical significance in protecting the great bulk of beaches and shorelines which are seasonally exposed to severe storm conditions. Moreover, the disclosed device is a permanent structure and may be generally effective along river banks or lake fronts, but not against the ocean during a storm, where storm waves with high wind action could undermine the structure from the rear and cause serious damage to nearby properties and buildings.
More recently, experimental installations of breakwaters made up of concrete modular units have been proposed in the prior art for preserving shorelines under either prevailing or variable ambient conditions. Such modular units, as described in U.S. Pat. Nos. 4,407,608 and 4,498,805, can be separately transported and assembled at the site into a unitary body. One substantial limitation of these prior structures is that they are not very effective during a coastal storm, where storm waves have been reported to approach heights of over 20 feet. Moreover, these breakwater structures are not sufficiently anchored to withstand severe wind and wave conditions and cannot be readily assembled without reliance upon heavy equipment.